This application claims priority under 35 U.S.C. .sctn..sctn.119 and/or 365 to "THE VARIABLE VALVE LIFT DEVICE," Application No. H09-248719 filed in JAPAN on Sep. 12, 1997, the entire content of which is herein incorporated by reference.
This invention relates to a variable valve lift device for varying the opening and closing timing or amount of lift of intake and exhaust valves.
Japanese Laid-Open Patent Publication No. H08-189316 published on Jul. 23, 1996 or corresponding U.S. Pat. No. 5,603,294 published on Feb. 18, 1997 discloses a conventional variable valve lift device. In these publications, a lifter is provided to slide inside a bore that is formed in a cylinder head of an engine. The lifter includes an outer body and an inner body. An upper end of the outer body is in contact with a high speed cam. An upper end of the inner body is in contact with a low speed cam. A restricting member is mounted on the outer body to slide in perpendicular direction with respect to a valve stem. The restricting member may restrict mutual movements between the outer and inner bodies when the restricting member is engaged with the inner body. Further, a control member is provided to control the slide action of the restricting member. The control member may select one of two modes. In the high lift mode, the control member engages the restricting member with the inner body. In the low lift mode, the control member disengages the restricting member from the inner body.
Japanese Laid-Open Patent Publication No. H08-42315 published on Feb. 13, 1996 discloses a conventional variable valve lift device. In this publication, a cylindrical member is provided to slide inside a bore that is formed in a cylinder head of an engine. The cylindrical member is driven by a cam. In the cylindrical member, a piston, a restricting member and locking member are provided. The piston receives fluid pressures and selects one of two positions to switch lifting amount of a valve. The restricting member may be displaced under spring force to restrict the lifting amount of the valve. The locking member deforms in accordance with a locus of the cam to hold the restricting member at a position.
However, in the above conventional valve lifters, it is hard to timely switch the lifting amount so that the restricting member may not operate smoothly.
In Japanese Laid-Open Patent Publication No. H08-189316, such switching timing depends on an application timing of the fluid pressure. Therefore, the restricting member may interfere with the inner body if such switching timing overlaps with the lifting timing of the cam. Such interference may generate noise to deteriorate durability of the valve lifter. Such interference may also happen when the valve lifter is at the bottom dead center because the lifter is driven by a nose area of the cam and the inner and outer bodies may receive different forces from the nose area.
In Japanese Laid-Open Patent Publication No. H08-42315, a channel is provided on the cam to detect a rotational position of the cam. Such detection may require a complex system to increase the cost of the valve lifter.
Accordingly, a feature of the present invention is to provide a variable valve lift device to solve the above conventional drawbacks.
Further, a feature of the present invention is to switch lifting amount in time.
Yet further, a feature of the present invention is to prevent the restriction member from interfering with the inner body.
To achieve the above features, a variable valve lift device provided in a bore of a cylinder head to open and close a valve in accordance with a rotation of a cam comprises:
an outer body driven by the cam and slidably provided in the bore; PA1 an inner body slidably provided in the outer body, the inner body being connected to the valve; PA1 a restricting member for restricting mutual displacement between the outer body and the inner body; and PA1 a synchronizing member slidably provided in the inner body and for controlling the restricting member based on inertia applied thereto.
In the present invention, the restricting member is controlled by the synchronizing member. The synchronizing member detects the acceleration of the inner body so that the restricting member may restrict the mutual displacement between the outer body and the inner body in a timely manner.